1. Field of the Invention
This invention relates generally to methods and apparatus for treating a fluidizable solid, such as natural and artificial sludges, having one or more dioxins absorbed or adsorbed thereon, leaving a relatively uncontaminated solid material. Dioxins include dibenzo-p-dioxin as well as its halogenated (particularly chlorinated) derivatives. More particularly, the present invention is directed to processes and apparatus for separation of dioxins from a fluidizable solid material so that the fluidizable solids can be returned to this source or otherwise used as non-hazardous materials. The separated dioxins, in relatively concentrated form, are easily disposed of, such as by burial or incineration.
2. Background and Prior Art
Polychlorinated biphenyls, or PCBs, were manufactured from 1929 to 1978. The manufacture of polychlorinated biphenyls has been banned in the United States since 1978. Similarly dioxin, particularly the chlorinated derivatives of which there are about 75 derivatives, has been a major hazard.
Dioxin (dibenzo-p-dioxin) is the most simple of all existing dioxins. There are, theoretically, 75 possible chlorinated species of dioxin alone. Some of the more common dioxins are 1, 3, 6, 8-tetrachlorodibenzo-p-dioxin; and 1,3,7,9-tetrachlorindibenzo-p-dioxin. Other halogenated dioxins are also theoretically possible.
A tremendous amount of these chemicals, suspected of causing cancer and birth defects, have been dumped over a number of years, either accidentally or deliberately, in an entirely reckless fashion. Dioxins are a significant hazard to the environment and their disposal has caused great concern. Incineration and land burial have been the main methods of dioxin disposal. The great volume of dioxin laden sludge for transportation and burial represents a tremendous cost for such dioxin disposal.
Because of the method of dumping toxic chemicals such as dioxins, a tremendous mass of soil has been contaminated. In the past, bottom soils or the like contaminated with these toxic organic fluids have been treated by attempting to burn or by burying them. Because of the nature of the materials in which the dioxin contamination is often found, burning is extremely difficult and burying is often only a stop gap measure.
It has been recognized that thermal decomposition of polychlorinated organic compounds is possible despite the very high degree of thermal stability of these compounds. U.S. Pat. No. 4,140,066 discloses a method of decomposing PCBs by exposure to heat in a combustion chamber which operates with extremely intense turbulence and pulsation under temperatures as low as 850.degree.C. and with residence times as short as 0.1 second. However, the patent provides no method or apparatus for dealing with the problem of the treatment of mountainous amounts of contaminated, wet material having a relatively low heating value.
A variety of techniques for incinerating waste material are known. The following U.S. Pat. Nos. are exemplary: 4,245,570; 3,858,534; 3,829,558; 3,812,794; 3,716,339; 3,511,194. A device such as the Williams U.S. Pat. No. 4,245,570 has been found to be effective in drying sewage sludge, but, prior to the present invention, has not been used to remove toxic chemicals such as dioxin from a fluidizable solid material, such as a sludge e.g., sand, clay, diatomaceous earth, charcoals, carbon, coals, silicas, alumina, silica-aluminas, metal particulates, metallic ores, and artificial sludges, such as those resulting from industrial spill absorption of liquids into an absorbent material.